Use of vegetative material as a filler in composite materials

ABSTRACT

The present invention provides a filler for use in composite materials wherein said filler comprises a vegetative-based material and wherein said vegetative-based material can be fresh or carbonised. In one particularly preferred embodiment the present invention utilises carbonised rice husk. In a further aspect of the present invention there is provided a process for the production of a carbonised vegetative-based filler wherein said process comprises burning a fresh vegetative-based material at about 800° C. for about 4 seconds.

RELATED APPLICATIONS

This application is a continuation application of U.S. application Ser.No. 09/889,610, entitled “Use of Vegetative Material as a Filler inComposite Materials”, filed Jan. 8, 2002, which is a continuationapplication of PCT/AU00/00018, filed Jan. 17, 2000 which published as WO00/42116, which claims priority to AU PP 8198 filed Jan. 18, 1999, allof which are incorporated herein by reference in their entirety.

TECHNICAL FIELD

This invention relates to the use of a filler derived from cereal husk,more particularly rice husk, in composite materials to enhance the flameretardant, antistatic, accelerator, plasticiser and blowingcharacteristics in various composite materials. The invention hasparticular but not exclusive application to the following families ofcomposites:

-   -   1. Thermoplastic Resins    -   2. Thermoset Plastics    -   3. Rubbers and Elastomeric Materials    -   4. Conductive Coatings and Printing Inks    -   5. Bitumen    -   6. Concrete

BACKGROUND ART

Composite materials are well known. Fillers are usually added tocomposite materials, including composite polymers, to save cost or toenhance a particular mechanical property or other characteristic of thematerials. The usage of fillers is usually accompanied by couplingagents that enhance the polymer-filler and filler-filler interaction sothat the expected properties are realised.

The present invention is concerned with fillers which enhance theanti-static, flame retardant, accelerator, plasticiser, blowingcharacteristic and/or other physical or mechanical properties ofcomposite materials and has particular application for use in compositepolymers. Such have wide application in the aeronautical, mining,computer, road building, textile, foot ware, rubber and polyurethaneindustries among others. For example, it is often desirable to preventthe build up of static charges which can cause sparks (and henceexplosions or electrical damage) or production problems, eg. collectionof dust and poor feeding of materials through machinery. More highlyconductive composite polymers can also be used for Electro MagneticInterference shielding, for example.

Carbon black fillers, aluminium flakes and fibres, stainless steelfibres and chopped carbon fibres have all been used as fillers for thepurpose of rendering composite plastic conductive. Likewise otherchemicals such as Halogen compounds or triethyl phosphate have been usedto achieve the flame retardant property.

A number of theories have been proposed to explain how discreet particlefillers impart conductivity and flame retardant properties in compositeplastics.

In order for current to flow in a conductive polymer compound, electronsmust travel along the filler as the plastic itself is an excellentinsulator. To achieve this flow the discreet particles of the fillermust be in contact or separate by a minimum distance which is probablyless than 100 Angstroms. There are three properties of the fillerparticles which will effect the average inter-particle distance for agiven filler loading in a polymer system. These are particle size, shape(structure), and porosity. Smaller size, irregular shape and highporosity all result in smaller inter-particle distances and hence higherconductivity. A fourth property of the particle which is relevant toconductivity and flame retardant properties in the composite plastics issurface chemistry, that is the presence of oxygen on the surface. Thepresence of appreciable quantities of oxygen on the surface (calledvolatile content) acts as insulation and hence reduces conductivity.

The known conductive fillers such as carbon black, aluminium, stainlesssteel and carbon fibres are expensive and furthermore some of thesematerials have other processing difficulties, eg. aluminium fibres andstainless steel fibres settle in liquid environments due to their highdensity. Further problems with known conductive fillers are that theyoften compromise other properties of composite plastics such as flameretardance and strength.

Static electrification of articles can lead to a number of undesirableeffects including:

-   -   Attraction of dust particles.    -   Attraction between surfaces, e.g. plastic films and textile        yarns.    -   Risk of fire or explosion caused by sparking near inflammable        liquids, gases, and explosive dusts, e.g. coal dust and flour.    -   Risk of shock to persons handling equipment.

The accumulation of electrostatic charges can be prevented by usingmaterials of low resistance. The resistivity of natural rubber can belowered by compounding with suitable ingredients. Alternatively, asstatic electrification is a surface phenomenon, the product can becovered with a conducting surface layer.

Low resistance rubber is required for a wide range of applications, suchas rollers for textile machinery, conveyor belting, fuel hoses,flooring, footwear, antistatic gloves (electronic industry), cables,equipment used in hospital operating theatres, and aircraft components.

The terms “antistatic” and “conductive” are restricted here to rubberproducts rather than the rubber itself because the electrical resistanceof the product depends not only on the resistivity of the rubber butalso on the shape and most probable positions of charge generation anddischarge.

Natural rubber is normally considered to be an electrically insulatingmaterial but it can be an electrically insulating material but it can becompounded to give electrical resistivity lying anywhere between 1ohm/cm. and 10¹⁵ ohm/cm. The most common means of reducing resistance isto add a suitable carbon black (super conductive furnace). Resistancefalls with a decrease in particle size, increase in black “structure”and increase in concentration. For light coloured products certaingrades of aluminium silicate may be used as antistatic fillers althoughthese are usually less effective in reducing resistance than the superconductive furnace. There are also other proprietary antistatic agentsthat are available, such as ethylene oxide, but still these agents areless effective then the super conductive furnace.

The applicant has found that carbonised rice husk is particularly suitedfor use as a filler in plastics as it has been found to enhance theconductivity and flame retardant properties of the composite plastics.

Honeycomb structure of a matrix is supposed to be one of the strongeststructures that have been determined by Structural Engineers. Thestrength comes about from the full depth hexagons and half-depthtrapezoids. This type of structures is presently used as designs forbuilding bridge decks.

The rice husk has a similar type of honeycomb design, which results innot only providing strength to the matrix, but also has sound andthermal insulation properties. The Sound insulation property is providedby the micro-cellular structures formed by the honeycomb structure inthe brown rice husk. Thus the sound is trapped within the micro-cellularstructure. This property is inherent to the brown (fresh) rice husk. TheThermal insulation property is provided by the honeycomb structure,which is strengthened by the silica and fibre which predominatelypresent in brown rice husk and lesser in the carbonised (depend to therate of carbonising) rice husk.

The presence of appreciable quantities of oxygen on the surface ofcarbonised rice husk acts as insulation for each aggregate, therebyreducing the conductivity and also reducing the flammability. Thepresence of nitrogen and oxygen in the fresh husk not only enables theblowing effect but also nitrogen being inert reduces the flame spread.”The volume of gas (nitrogen/oxygen) evolution per gram of fresh ricehusk is 240 ml/g. The husk's decomposition temperature is at about 280°C. and curing temperature of rubber and ethyl vinyl acetate is between130° C.-180° C., thus when urea (dinitroso pentamethylene tetramine) ismilled along the decomposition temperature is reduced within the curingtemperatures. The presence of silica in the rice husk provides bettermechanical strength.

Typical chemical and physical properties of fresh and carbonised ricehusk are detailed as follows:

-   -   consists of 20-23% of paddy    -   husk burning: 20% ash by weight    -   90-95% is silica (amorphous and crystalline)    -   physical characteristics: bulk density 96.12-112.14 kg/m³    -   pH 7.14 (husk ash)    -   moisture content 5.6-7.2%, dry basis

ash 22.2% Chemical Composition Moisture Content: 5.6-7.2%, dry basisAsh: 22.2% Protein  2.4% Crude fat  0.7% Carbohydrate 32.0%, Fresh RHCarbonised RH Al₂O₃ 0.025%  0.023% CaO 0.36%  0.12% NaO 0.034%  0.018%Si0₂ 96.2% 53.88% Fe₂0₃ 0.041%  0.022% MgO 0.16% 0.078% K₂O 0.69%  0.95%P₂O₅ 0.57%  0.27%

It is an object according to one aspect of the present invention toprovide an alternative filler which will enhance the antistatic, flameretardant, accelerator, plasticiser blowing and/or other physical ormechanical in composite materials. The filler is desirably cheap,environmentally friendly and replenishable and it does not compromiseother characteristics of the composite material.

SUMMARY OF THE INVENTION

The present invention in one aspect resides in the use of carbonisedvegetative-based filler to provide improved antistatic, flame retardant,accelerator, plasticiser, blowing and/or other physical or mechanicalcharacteristics in composite materials.

Preferably, the carbonised vegetative-based filler is carbonised ricehusk.

Preferably, the carbonised rice husk is burnt at about 800° C. for about4 seconds. Most preferably, the carbonised rice husk is burnt at803-804° C. for 3-4 seconds.

In another aspect the invention resides in a composite material, moreparticularly a composite plastic including a vegetative-based fillerwhen used as a conductive or flame retardant article.

Preferably, the carbonised vegetative-based filler is carbonised ricehusk which has been burnt at 803-804° C. for 3-4 seconds.

The present invention also exhibits the usage of fresh and carbonisedrice husk as a blowing agent when used in combination with recycled(reclaimed), or virgin natural rubber or other suitable thermoplasticmaterials. Though other conventional blowing agents have been used withnatural or synthetic rubber to achieve the similar products but so farno blowing agents have been used with recycle (reclaim) rubber toproduce similar products. Furthermore the conventional blowing agentsare expensive and dosages are higher as compared to the fresh rice husk.For example for the conventional blowing agent, the dosage is about6.5-7 phr, whereas the fresh/carbonised rice husk, the dosage is between1.5 to 3 phr. When rice husk is used at different dosages the blowingeffect is different. It was also noted that the rice husk does not onlywork as a blowing agent, but also as a plasticizer and a filler. Theproperties achieved are comparable to conventional blowing agents, whenusing fresh or carbonised rice, has no difference to the conventionalblowing agent other than the colour of the end product.

Ebonite, a hard, dark-coloured plastic-like material, is the reactionproduct of rubber and a large proportion of sulphur. Simplerubber/sulphur mixtures are seldom used in practice; they suffer frompoor processability, require long cure times and lead to excessiveshrinkage and heat evolution during cure. Accelerators, fillers,processing aids and other compounding ingredients are widely used inebonite, as in soft rubber vulcanised rubber, to ease processing,shorten cure times and modify properties. The curing times for eboniteare generally up to ten (10) hours at 150° C., thus making eboniteproducts expensive. Ebonite can be made from synthetic, such as BR, NBR,SBR and Nitrile rubber and as well as from Natural rubber. Highstrength, low thermal conductivity, chemical resistance and insulatingproperties of natural rubber make it a popular choice. Although it hasbeen superseded in many applications by synthetic thermoplastic andthermosets, it is still used for outstanding chemical resistance andelectrical properties coupled with high mechanical strength and ease ofmachining.

The present invention exhibits the usage of fresh and carbonised rice asan accelerator when used in combination with recycled (devulcanised) orvirgin natural rubber, and at the same time making ebonite a conductiveproduct when carbonised rice husk is used. Though other conventionalaccelerators have been used with natural or synthetic rubber (virgin orrecycled) to achieve the similar products but so far no acceleratorslike the rice husk material have been used with recycled (devulcanised)rubber to produce similar products. Further more the conventionalaccelerators and conductive carbon black are expensive and difficult toblend and process. When rice husk is used singularly at differentdosages the activation effect is different to meet industrialrequirements. Generally for ebonite production the sulphur contentshould be in the range of 25-40 phr, but whereas when fresh rice huskbetween 25-30 phr is used the sulphur content could be reduced to 20-25phr. Accelerators are less effective in ebonite than in soft rubber andlarge quantities are generally required. Basic accelerators such asguanidines and aldehyde-amines are preferred. Inorganic activators suchas magnesium oxide, magnesium carbonate and lime are also effective whenused with organic accelerators to reduce cure time without the risk ofover heating.

Common inorganic fillers used in ebonite are china clay, talc, silica,whiting and magnesium oxide. These also reduce shrinkage and heatevolution but loaded ebonite generally have weaker mechanical propertiesthan unloaded ones. Carbon black does not reinforce ebonite and isnormally only added for pigmentation, although conductive carbon blackare sometimes used to prepare electrically conducting ebonite.

BEST MODE

Following is an example of the invention, in this example the filler iscarbonised rice husk (CRH) which has been burnt at 803-804° C. for 3-4seconds. After this the CRH is obtained.

The manner in which the rice husk is burnt is believed to be importantin achieving the desired surface area, surface structure and porositynecessary for conductivity and flame retardant and blowing properties inthe composite plastics to be achieved. At this stage the range oftemperature and the duration of the time of burning which achieves thedesired result has not been fully explored, however it is predicted thatthe temperature range will be from about 100-950° C. and the time rangewill be from about 2=30 seconds, although these ranges may be muchnarrower. The importance of controlled burning in a prescribed timeresults in obtaining better surface area and porosity which in turnoffers ideal properties emitting anti-static, flame retardant andenhancing physical properties of the material. In the absence ofcontrolled burning, the surface area, surface structure and porositywould be distorted. While the present exemplification involves use ofcarbonised rice husk it is possible that the desired results may beachieved by use of other carbonised vegetative-based fillers.

EXAMPLE 1

A thermoset application called pulforming was used to manufacture fibrereinforced bolts. Fibre glass tows (36 tow of 8000 tex) are pulled intoa resin bath that contains:

-   -   1. Polyester and Vinyl Ester combination, ie. 60% Vinyl Ester        (Derakane 411—Dow Chemical) and 40% Polyester (Everpol 3260        AR-P.T. Arinde).    -   2. Zinc Stearate (mould releasing agent)—1.18% of the resin        weight BYK 980 (improves wetting and dispersing of fillers in        glass fibre reinforcement compounds)—1.5% of the filler weight.    -   3. BYK 515 (air releasing agent)—0.5% of the total weight of the        resin mixture.    -   4. BYK 996 (wetting and dispersing additive for mineral fillers        in hot curing, glass fibre reinforced UP-resin systems)—2% of        the resin weight.    -   5. Fillers (Ca₂(CO)₃ & Carbonised Rice Husk (mesh size 325) @        55% & 12% of the resin weight).    -   6. Aluminium Trihydrate (2.4% of the resin weight).    -   7. Catalyst TBPH (Tertiary Butyl Peroxy-2-Ethyl Hexanoate)        -   2.12% of the resin weight.        -   TBPB (Tertiary Butyl Perbenzoate)        -   0.53% of the resin weight.

The wet fibre glass tow is pulled into the mould and compressed at apressure of 800 psi (5600 kPa) for 3.8 minutes at 130° C. Then the boltis pulled out of the mould and left to cure.

The following day tests were carried out on the bolt with the followingresults:

-   -   Tensile strength at the thread—50 kN    -   Torque—45 ft/lb    -   Bond strength—BS 1610:Part 1, Grade 1.0    -   Fire rating—BS 5865:1980—Persistence flame shall be less than 10        seconds    -   Electrical conductivity—less than 10 to the power of 9 Ohms.

EXAMPLE 2

All chemicals used are taken by percentage of weight of rubber. Therubber and the chemicals are mixed in a Banbury, for 5 minutes. Recycledrubber (reclaim) (220 g) is first milled with zinc oxide(4.5%)—accelerator, which is followed with stearic acid(1.8%)—activator, Mercadibenzothiazole disulphide (MBTS)(0.5%),Tetramethylthiuram disulphide (TMTD)(0.2%)—accelerator, fresh rice husk(27%)—blowing agent and filler and sulphur (2.7%)—vulcanisate. Then themixed compound is milled for five (5) minutes to form a sheet that isready for curing. Then a piece of the sheet weighing about 32 g isplaced in a mould that it is to be cured for two (2) minutes in a ovenat 150° C. temperature. The conventional curing time is six (6) minutesat the same temperature of 150° C.

The rubber and the chemicals are mixed in a Banbury, for 5 minutes. Thesimilar approach has been done for using SBR Rubber (100 g), silica (62g), Peg 1500 (2.5 g), Paraffin oil (5 g), Zinc oxide (2.5 g), Wing stay(0.5 g), Wax (1 g), Mercadibenzothiazole disulphide (MBTS) (1.5 g),Tetramethylthiuram disulphide (TMTD) (0.2 g), Stearic acid (1.5 g) andSulphur (2 g). The milling was done for ten (10) minutes and later curedin the oven for six (6) minutes at 150° C.

This exercise was repeated by using fifty (50) percent of the virginmaterial compound and fifty (50) percent recycled (reclaimed) materialcompound, and cured in the oven at 150° C. for two (2) minutes.

With the level, of rice husk dosage, the blowing effect can becontrolled to suit the industry's requirement.

Machine Operating Conditions

Virgin Rubber: TYRE DUST WITH EXAMPLE EXAMPLE BROWN 1 WITH 1 PROP- SMR-TYRE RICE BROWN WITHOUT ERTIES 10 DUST HUSK RICK HUSK BROWN Mooney 6036.6 31.8 24 30 Viscosity MLI + 3, 100° C. Monsanto Rheometer, 150° C.Scorch time 1.4 3.8 1.2 2 2.5 Cure time 7.4 3.5 3.25 4 4By using rice husk the Mooney viscosity was lower than the conventionalfiller, thus lowering scotch time (time taken by the rubber compound toflow into the mould) and curing time (time taken to cure rubbercompound) respectively. As such this leads to a cheaper productionsystem. Presently various fillers and blowing agents are being used inthe production of soft/spongy rubber that would produce different typesof cell structures for an end product, but the cost determines themarket.

EXAMPLE 3

All chemicals used are taken by percentage of weight of rubber. Therubber and the chemicals are mixed in a Banbury, for six (6) minutes.The recycle (devulcanised) rubber is first milled with magnesium oxide(2%)—accelerator, which is followed with Diphenylguanidine(2%)—accelerator, fresh rice husk (30%)—accelerator and filler andsulphur (30%)—vulcanisate. After the milling at the Banbury for ten (10)minutes, it is then milled into a sheet. The mould was heated in theoven press to 150° C. then the sheeted rubber is placed in the mould andit is cured for twelve (12) minutes. The conventional curing time isbetween eight to ten hours at the same temperature of 150° C.

A conventional formula for ebonite was selected to compare. The rubberand the chemicals are mixed in a Banbury, for 5 minutes. The similarmixing as above was followed, using SBR 5 Rubber (100 g), ebonite dust(100 g), China clay (50 g), Magnesium oxide (5 g), Diphenylguanidine (3g), Linseed oil (5 g) and Sulphur (45 g). The milling was done for ten(10) minutes and later cured in the oven for eight (8) hours at 150° C.

Mix Properties; Rice Husk Filled Mix Mooney viscosity, MLI + 3, 100° C.24 Mooney viscosity, MLI + 3, 120° C. 18.5 Mooney scorch, t₅, MLI + 3,120° C. min. 5.8 Monsanto Rheometer, 160° C. 110 time to 95%cross-linking, s

By using rice husk the curing time is reduced tremendously twelveminutes as compared to eight to ten hours. The sulphur content in therubber polymer is reduced by fifteen percent.

The results are based on cure time, the formulation with rice husk curesfaster than the formulation without rice husk, i.e. twelve minutes forwith brown rice husk and about eight hour without rice husk.

EXAMPLE 4

All chemicals used are taken by percentage of weight of natural rubber(NR). The natural rubber and the chemicals are mixed in an open mill orkinder, for six (6) minutes. Natural rubber is first milled with stearicacid (1%) and zinc oxide (5%) activator, which is followed with ricehusk (blowing agent) (2.5-3.5%), calcium carbonate—(40%), promoter—ureabased (2.5-3.5%), silica (10%), accelerator dibenzthiazyldisulphide(MBTS) (0.05%) and catalyst sulphur (1.5%). After the milling at theopen mill or kinder for ten (10) minutes, it is then milled into asheet. The mould was heated in the oven press to 160° C. then thesheeted natural rubber is placed in the mould and it is cured fortwenty-two (22) minutes.

The temperature for curing could be from 145°-160° C. and the cure timemay differ according to the mould size.

Cured Properties; Rice Husk Filled Blowed Mix—Micro-Cellular Cells. 1.Hardness Askar C 35 2. Shrinkage %  5 3. Specific Gravity g/cc 0.3-0.35

By using rice husk as a blowing agent the catalyst percentage could bereduced and as well as the percentage of blowing agent used.

EXAMPLE 5

Thermoplastic (EVA)

All chemicals used are taken by percentage of weight ofthermoplastic—Ethyl Vinyl Acetate (EVA). The EVA and the chemicals aremixed in an Open Mill or Knider, for six (6) minutes. Ethyl VinylAcetate (EVA) is first milled with Stearic Acid (1%) and zinc oxide (5%)accelerator, which is followed with Rice Husk (Blowing agent) (2.5%).Magnesium carbonate—(10%), Promoter—urea based (5%) and catalyst DiacylPeroxide (1%). After the milling at the Open mill or Knider for ten (10)minutes, it is then milled into a sheet. The mould was heated in theoven press to 160° C. then the sheeted EVA is placed in the mould and itis cured for twenty-two (22) minutes.

The temperature for curing could be from 145°-160° C. and the cure timemay differ according to the mould size.

Cured Properties: Rice Husk Filled Blowed Mix—Micro-Cellular Cells 1.HARDNESS Askar C 29-35 2. SHRINKAGE % 2 3. SPECIFIC GRAVITY g/cc 0.2004. COMPRESSION SET % 80

By using rice husk as a blowing agent the catalyst percentage could bereduced and as well as the percentage of blowing agent used.

EXAMPLE 6

The rice husk is mixed by weight with tyre crumbs (35-40 mesh) and aneffluent from the palm oil mill called Scavenger (which have a fattyacid content (C₈ C₁₈). From literature it has been reported that byusing tyre crumb with the binder (bitumen) there is an improve dfproperties for the asphalt mixture. This invention not only uses tyrecrumb along with rice husk and an oil palm effluent to further improvethe properties. As well as the formulation address the recyclability ofall agro waste by-products to be used in the road surfacing industries.The formulation of the rice husk mixture as follows: Rice husk 50% Tyrecrumb 45% Scavenger  5%

In this particular example the usage of rice husk mixture is dividedinto two categories:

-   -   A. RICE HUSK MIXTURE USED IN MODIFIED BINDER    -   B. RICE HUSK MIXTURE USED IN AS FILLER

A. The rice husk mixture is added to the bitumen first in compliance tothe SOCIETY OF HIGHWAY PROCEDURE (SHRP) to manufacture modified bitumen.The bitumen is first heated to about 160° C., then the rice husk mixturetwenty percent 20% by weight of bitumen is mixed with the heated bitumenfor about one hour. As a result of this reaction a modified bitumen ismade. From here 5-7% by weight of this modified bitumen is added to theaggregate. The aggregate is first heated to about 200° C. and themodified bitumen is mixed for three to four minutes. The modifiedbitumen with rice husk mixture complies to all requirement of the SHRP.

B. The rice husk mixture is added as a filler to the aggregate, by four(4%) by weight to the aggregate weight. The aggregate is first heated to200° C., and is allowed to cool to about 160° C., then the rice huskmixture is added and mixed and lastly the bitumen 5-6% by weight ofaggregate is added and mixed for 3-4 minutes. This blending with ricehusk mixture complies to all requirement of the Marshall Properties.TABLE 1 PROPERTIES OF RICE HUSK MODIFIED BINDER - SHRP RICE SHRP 80/100HUSK MIXTURE FLASH POINT TEMP. ° C. 230    240 SOFTENING POINT, ° C.44-50 55-70 PENETRATION @ ° C. 25, dmm  80-100  60-100 BROOKFIELDVISCOSITY @ <500 >1500 135° C., MPaS DYNAMIC SHEAR RHEOMETER PG 70ORIGINAL G*(Pa) <1000 >1200 δ(°) >80  >80 G*/Sin δ <1000 >1200 AFTERRTFOT G*(Pa) <1000 >3800 δ(°) >80  >70 G*/Sin δ <1000 >3800 AFTER PAVG*(Pa) <1000  >230 δ(°) >80  >50 G*/Sin δ <1000  >260 PG76 ORIGINALG*(Pa) <1000 >1800 δ(°) >80  >70 G*/Sin δ <1000 >1800 AFTER RTFOT G*(Pa)<1000 >2400 δ(°) >80  >70 G*/Sin δ <1000  >2600, AFTER PAV G*(Pa) <1000 >230 δ(°) >80  >50 G*/Sin δ <1000  >280

TABLE 2 MIXED PROPERTIES OF RICE HUSK MODIFIED BINDER PROPERTIES 80/100RICE HUSK MIXTURE MARSHALL STABILITY (kN)  5-10  >13 FLOW (mm) 2-4 2-4QUOTIENT (kN/mm)   1-3.5 3-4 RESILIENT MODULUS @ 25° >2000 >2800

TABLE 3 MIXED PROPERTIES OF RICE HUSK MIXTURE AS FILLER PROPERTIES80/100 RICE HUSK MIXTURE MARSHALL STABILITY (kN)  6-10  >12 FLOW (mm)2-4 2-4 QUOTIENT (kN/mm)   1-3.5 3-4 RESILIENT MODULUS @ 25° >2000 >2800

TABLE 4 PREFERRED PARTICLE SIZE AND DOSAGE OF FRESH AND/OR CARBONISEDRICE HUSK FOR PARTICULAR COMPOSITE MATERIALS COMPOSITE MATERIALFRESH/DOSAGE CARBONISED/DOSAGE BITUMEN (MECHANICAL   100 MESH - 40-60phr — PROPERTY THERMOPLASTIC (EVA) 325-400 MESH - 1.5-2.5 phr 325-400MESH - 1.5-2.6 phr BLOWING CHARACTER THERMOPLASTIC (EVA) 325-400 MESH -1.5-5 phr 325-400 MESH - 1.5-2.5 phr MECHANICAL PROPERTY RUBBER(N.R./S.R.) 325-400 MESH - 1.5-27 phr 325-400 MESH - 1.5-27 phr BLOWINGCHARACTER EBONITE N.R. 100-200 MESH 18-30 phr — (REDUCE CURE TIME)RUBBER (N.R./S.R.) 100-200 MESH 5-10 phr 100-200 MESH 5-10 phr SCOTCHTIME THERMOSET RESIN —   325 MESH 10-15 phr (FLAME PROPERTY) THERMOSETRESIN 100-200 MESH 10-15 phr 100-200 MESH 10-15 phr (MECHANICALPROPERTY) THERMOSET RESIN — 325 MESH 10-15 phr (ANTISTATIC) RUBBER-LATEX(N.R./S.R.) — 325-400 MESH 5-15 phr ANTISTATIC RUBBER (N.R./S.R.) —325-400 MESH 5-15 phr ANTISTATIC CONCRETE 100-200 MESH 10-15 phr 100-200MESH 10-15 phr (MECHANICAL PROPERTY)N.R.—NATURAL RUBBERS.R.—SYNTHETIC RUBBER

It will of course be realised that whilst the above has been given byway of illustrative examples of this invention, all such and othermodifications and variations hereto, as would be apparent to personsskilled in the art, are deemed to fall within the broad scope and ambitof this invention as herein set forth. For instance, while the precedingexamples relate to the use of fresh and/or carbonised rice husk it wouldbe apparent to a person skilled in the art that other cereal husks suchas sorghum husk may be suitable.

Throughout the description and claims of the specification wherereference is made to the dosage of fresh and/or carbonised rice husk,this dosage is expressed in terms of “phr” (parts per hundred) based onthe weight of the composite material into which the rice husk is beingintroduced.

Throughout the description and claims of the specification the word“comprise” and variations of the word, such as “comprising” and“comprises”, is not intended to exclude other additives, components,integers or steps.

The claims are:

1. A filler for use in composite materials wherein said filler comprisescarbonized vegetative-based material wherein said carbonizedvegetative-based material is the product of burning freshvegetative-based material at 803° to 804° C. for 3 to 4 seconds.
 2. Afiller according to claim 1 wherein the carbonized vegetative-basedmaterial is carbonized rice husk.
 3. A filler according to claim 1wherein the fresh vegetative material is ground to a particle size offrom 100 mesh to 400 mesh.
 4. A method for improving the anti-static,flame retardant, accelerator, plasticiser and/or blowing characteristicsof a composite material wherein said method comprises blending into thecomposite material with a carbonised vegetative-based filler accordingto claim 1 and wherein said blending is substantially completed prior toincorporation of any additives, if any.
 5. A method according to claim 4wherein the carbonised vegetative filler has a particle size of from 100mesh to 400 mesh.
 6. A method according to claim 4 wherein saidcomposite material is selected from the group comprising: i)thermoplastic resins; ii) thermoset plastics; iii) rubbers andelastomeric materials; iv) conductive coatings; v) printing inks; vi)bitumen; and vii) concrete.
 7. A composite material having improvedanti-static, flame retardant, accelerator, plasticiser and/or blowingcharacteristics wherein said composite material is produced by themethod of claim
 7. 8. A method for improving the flame retardant abilityof a thermoset resin said method comprising blending carbonised ricehusk according to claim 2 into said thermoset resin.
 9. A methodaccording to claim 8 wherein the carbonised rice husk has a particlesize of 325 to 400 mesh and the dosage of carbonised rice husk isbetween 10 to 15 parts per hundred.
 10. A method for improving themechanical properties of thermoset resins including tensile and torquestrength, said method comprising blending carbonised rice husk accordingto claim 2 into said thermoset resin.
 11. A method according to claim 10wherein the rice husk has a particle size of between 100 to 200 mesh andthe dosage of rice husk is between 10 to 15 parts per hundred.
 12. Amethod for improving the anti-static properties of a thermoset resinsaid method comprising blending carbonised rice husk according to claim2 into said thermoset resin.
 13. A method according to claim 12 whereinthe carbonised rice husk has a particle size of between 325 to 400 meshand the dosage of carbonised rice husk is between 10 to 15 parts perhundred.